The present invention is directed to bicycle brakes and, more particularly, to a center-pull style bicycle brake with synchronized brake arms.
Typical center-pull bicycle brakes comprise first and second brake arms pivotably mounted to a bicycle frame member such as front fork or rear seat stay of the bicycle frame. Each brake arm includes a brake arm mounting portion for mounting the brake arm to the bicycle frame member, a brake pad mounting portion, and a control interface portion. The brake arm mounting portion is disposed between the brake pad mounting portion and the control interface portion such that the brake pad mounting portion is disposed below the brake arm mounting portion when the brake arm is mounted to the bicycle frame member. When the first and second brake arms are mounted to the bicycle frame member, the control interface portion of the first brake arm extends to the side of the bicycle frame member at which the second brake arm is mounted, and vice versa. First and second return springs usually are mounted between the respective first and second brake arm mounting portions and the bicycle frame member for biasing the first and second brake pad mounting portions away from the bicycle wheel rim.
After the first and second brake arms are mounted to the bicycle frame member, an intermediate control element such as a control wire is mounted to the first control interface portion of the first brake arm and to the second control interface portion of the second brake arm. A primary control element then is mounted to the center of the intermediate control element such that, when the primary control element is pulled upwardly, the first and second brake arms rotate against the biasing forces of the first and second return springs so that first and second brake pads mounted to the first and second brake pad mounting portions frictionally contact the bicycle wheel rim.
The friction caused by the structures used to mount the first and second brake arm mounting portions to the bicycle frame member sometimes is not equally balanced between the first and second brake arms. As a result, the rotation of the first and second brake arms is not properly synchronized, so the first and second brake pads do not contact the bicycle rim at the same time. Several attempts have been made to solve this synchronization problem. For example, JP 62-177592 discloses first and second gear wheels that engage gear teeth on the first and second brake arms to synchronously push the control interface portions of the first and second brake arms apart during operation of the brake; JP 63-112995 discloses first and second rollers respectively mounted to the first and second control interface portions of the first and second brake arms, wherein a cam mounted to the primary control element contacts the first and second rollers to synchronously push the first and second control interface portions of the first and second brake arms apart when the primary control element is pulled upwardly; JP 64-90890 discloses a pair of links with attached rollers that are pushed apart by a cam mounted to the primary control element, wherein the rollers synchronously push the first and second control interface portions of the first and second brake arms apart when the primary control element is pulled upwardly; JP 64-90891 discloses multiple links connected both in series and in parallel to the first and second brake arms and to the primary control element to synchronously push the first and second control interface portions of the first and second brake arms apart when the primary control element is pulled upwardly. However, such complicated structures add more friction and operating effort to the braking device, which only gets worse when the synchronizing assemblies are subjected to water, dirt, mud and other contaminants.
Another disadvantage of prior art braking systems is that the biasing forces of the return springs must be overcome by the rider in order to operate the brakes. When synchronizing structures are used to synchronize the operation of the first and second brake arms, stronger return springs must be used to generate the greater biasing forces needed to overcome the additional friction created by the synchronizing structures and rotate the first and second brake arms so that the first and second brake pads are separated from the wheel rim. Such additional biasing forces further increase the effort required by the rider to operate the brakes.